This invention relates to circuitry for selectively actuating instrumentation circuits of an electrical musical instrument and, more particularly, to such circuitry used as an automatic rhythm generator.
Automatic rhythm playing or generating systems for use with electronic organs or similar instruments are well known in the art. Examples of such circuits are shown in a large number of United States patents including U.S. Pat. No. 3,548,065 of Freeman issued Dec. 15, 1970, to Chicago Musical Instrument Co., now Norlin Music, Inc., the assignee of the present application; U.S. Pat. No. 3,553,334 of Freeman issued Jan. 5, 1971, to Chicago Musical Instrument Co.; U.S. Pat. No. 3,567,838 of Tennes issued Mar. 2, 1971, to Hammond Corporation; U.S. Pat. No. 3,760,088 of Nakada issued Sept. 18, 1973, to Nippon Gakki Seizo Kabushika Kaisha; U.S. Pat. No. 3,763,305 of Nakada et al. issued Oct. 2, 1973, to Nippon Gakki Seizo Kabushiki; U.S. Pat. No. 3,764,722 of Southard issued Oct. 9, 1973, to C. G. Conn Ltd.; and U.S. Pat. No. 3,840,691 of Okamoto issued Oct. 8, 1974, to Nippon Gakki Seizo Kabushiki. Reference may be had to these patents for a detailed description of the different types of circuitry and the various techniques by which rhythm signals and tones may be automatically generated.
Briefly, all such circuits employ a plurality of rhythm voice or instrumentation circuits which produce tone signals respectively corresponding to a plurality of different musical instruments and suitable circuitry for actuating preselected ones of the instruments during selected ones of a succession of rhythm cycles. The tempo or rate at which the rhythm cycles are generated is customarily established by an oscillator or rhythm clock which is variable in frequency. In such circuits, different rhythm patterns are selected through means of manually actuateable switches to choose different rhythm patterns such as rhythms for a march, tango, swing, cha-cha-cha, rock. The different instrumentation circuits simulate different percussion instruments such as blocks, bass drum, brush, cymbal, snare drum, etc. or even non-percussion instruments.
Depending upon the rhythm pattern selected, none, one or plural instrumentation circuits are actuated during each rhythm cycle. For example, with the rhythm pattern for swing selected, the bass drum and brush instrument circuits may be actuated on the first rhythm cycle, no instruments actuated during the second and third rhythm cycles, the snare drum actuated during the fourth rhythm cycle, no instrument actuated during the fifth rhythm cycle, the brush instrument again actuated on the sixth rhythm cycle and so on in like manner for the next six rhythm cycles.
Each of the instrumentation circuits require a drive pulse applied thereto of appropriate width for proper actuation. Typically, each of the instrumentation circuits comprises a band pass filter having a high Q characteristic that produces an exponentially decaying sine wave on its output having a frequency equal to the resonant frequency of the filter. This sine wave output of each instrumentation circuit is produced when a rectangular wave drive pulse is applied to its input. The width of the input drive pulse should be approximately equal to one-fourth the period of the resonant frequency, for a drive pulse of this width when applied to the instrumentation circuit, will result in an output signal of optimum characteristics with regard to amplitude and distortion.
In known automatic rhythm systems, drive pulses of suitable width have been provided by means of monostable multivibrators or other suitable pulse shaping circuits. The monostable multivibrators, in turn, are driven by pulses of arbitrary widths without regard to the needs of the instrumentation circuit.
Disadvantageously, such monostable multivibrators and pulse shaping circuits are not readily amenable to embodiment in integrated circuit form together with the other parts of the automatic rhythm generator circuitry. Accordingly, the cost reducing and other benefits derived by providing the entire automatic rhythm generator circuitry in integrated circuit form have not heretofore been obtained.